LONG-TERM DEBT - SCHEDULE OF LONG-TERM DEBT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt	$ 2,103	$ 2,569
Less debt issuance costs	(12)	(15)
Less current portion	486	307
Long-term debt, net of current portion	$ 1,617	$ 2,262
Weighted-average fixed-interest rate	4.10%	4.20%
Weighted-average variable-interest rate	3.90%	2.80%
Proceeds from issuance of long-term debt, net of issuance costs	$ 339	$ 0	$ 2,044
Long-term debt payments	807	397	$ 249
Repayments of debt	451
Long-term Debt, Fiscal Year Maturity [Abstract]
2019	488
2020	305
2021	263
2022	216
2023	262
Thereafter	579
Long-term Debt	2,113
Fixed-rate notes payable due through 2028
Debt Instrument [Line Items]
Long-term Debt	642	959
Variable-rate notes payable due through 2028
Debt Instrument [Line Items]
Long-term Debt	$ 1,473	$ 1,625